Optical switching device and parallel processing architecture

ABSTRACT

A multiple-faced optical device comprising a light-responsive element having multiple faces, at least two of the faces constituting input faces for receipt of non-collinear light signals and at least one of the faces other than the input faces constituting an output face from which light signals transmitted through the light-responsive element are emitted. The light-responsive element is further configured to have optically-induced non-linear susceptibility to light signals transversely propagated through the light-responsive element such that at least one portion of the light-responsive element switches between two stable optical states in dependence on the total intensity of the light signals within the light-responsive element. The above-described optical device can be configured to perform various operations, such as AND/OR and INVERT/PASS logic operations, data line branching, signal time delay, and memory storage. An array of such devices provides parallel logic processing on a plurality of parallel optical data paths.

BACKGROUND OF THE INVENTION

The present invention relates generally to optical logic processing, andmore particularly to digital optical processing devices and computerarchitectures suitable for large scale parallel processing.

Bistable optical or opto-electronic logic devices have been developedwhich are capable of performing basic logic operations (e.g., AND, OR,NAND, NOR) and to perform various combinational logic. Examples of suchdevices are disclosed in U.S. Pat. Nos. 3,431,437 to Kosonocky;4,128,300 to Stotts et al.; 4,262,992 to Berthold, III; and 4,382,660 toPratt, Jr. et al. Fabry-Perot cavities responsive to collinear inputsignals have also been developed which exhibit high-speed switching andthe ability to perform logic operations. See "The Optical Computer," E.Abraham, C. T. Seaton S. D. Smith, Sci. Amer. Feb., 1983, pp. 85 etseq.; "Selected Papers on Optical Computing," H. J. Caulfield, G. Gheen(eds.), SPIE 1142, pp. 79 et seq.; "Optical Bistability: ControllingLight With Light," H. M. Gibbs, Academic Press, 1985; "From OpticalBistability Towards Optical Computing, The EJOBP," P. Mandel, S. D.Smith, B. S. Wherrett (eds.), North Holland, Elsevier SciencePublishers, 1987; "Optical Computing, A Survey for Computer Scientists,"D. G. Feitelson, MIT Press, 1988, pp. 147 et seq.; "Optical Computing88," J. W. Goodman, P. Chavel, G. Roblin (eds.), Proc. SPIE, 963 (1989),pp. 15 et seq., 138 et seq.

The development of a digital computer employing optical logic elementsis desirable because optical switching and gate elements are capable ofoutperforming their electronic counterparts in particular areas whichare essential in the development of improved computing devices.Specifically, optical switching and gate elements have the potential toprovide, inter alia, high speed, large scale parallel processingcapabilities.

However, the bistable optical logic elements and computer architecturesusing such elements which have heretofore been developed have not takenfull advantage of the features of nonlinear material nor of theintrinsic parallel nature of optical signal processing.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide opticaldigital logic devices and computer architectures which provide purelyoptical high speed parallel processing.

It is a further object of the present invention to provide optical logicelements responsive to non-collinear input signals and capable ofperforming different selected logic functions in dependence on aprogrammable optical control signal.

It is another object of the present invention to provide an array ofoptical logic elements which is particularly adapted to provideprogrammable parallel processing.

It is still another object of the present invention to provide anoptical parallel memory architecture which is capable of large-scalesimultaneous transfer of stored data using a single optical read signal.

These and other objects are achieved in accordance with one aspect ofthe present invention by a multiple-face optical element comprising alight-responsive element multiple faces. At least two of the facesconstitute input faces for receipt of non-collinear light signals and atleast one of the faces other than the input faces constitutes an outputface from which light signals transmitted through the light-responsiveelement are emitted. The light-responsive element is further configuredto have optically-induced non-linear susceptibility to light signalstransversely propagated through the light-responsive element such thatat least one portion of the light-responsive element switches betweentwo stable optical states in dependence on the total intensity of thelight signals within the light-responsive element.

In accordance with a further aspect of the present invention, aprogrammable optical logic array device for parallel processing of atleast one set of first and second non-collinear optical data signalsalong first and second data paths comprises an AND/OR optical gatecontrollable by a first optical program signal for selectively operatingin an AND/OR logic mode to produce corresponding first AND/OR seconddata output signals in dependence on the combination of data inputsignals present and the logic mode selected; a PASS/INVERT optical gateresponsive to one of the first and second data output signals from theAND/OR optical gate and controllable by a second optical program signalfor selectively operating in PASS or INVERT modes wherein, respectively,a PASS data output signal is produced in the same data path when the oneof the first and second data output signals is present and an INVERTdata output signal is produced in a different data path when the one ofthe first and second data output signals is not present; and a BRANCHINGoptical gate responsive to the PASS and INVERT data output signals fromthe PASS/INVERT optical gate and controllable by a third program signalfor selectively operating to transfer PASS/INVERT data output signalsapplied as inputs along the same data path as, or a different data pathfrom, the one on which the applied PASS/INVERT signal was travellingprior to transfer.

These and other objects, features and advantages of the presentinvention are described in or apparent from the following detaileddescription of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments will be described with reference to theaccompanying drawing, in which like elements have been denoted with likereference numbers, and wherein:

FIGS. 1A-1D are diagrammatic illustrations of exemplary embodiments of amulti-faceted optical element in accordance with the present invention.

FIG. 2 is a representation of a single valued response to total lightintensity of the optical element shown in FIGS. 1A-1D.

FIG. 3 is a representation of a hysteresis response to total lightintensity of the optical element shown in FIGS. 1A-1D.

FIG. 4 is a diagrammatic illustration of a programmable AND/OR gateembodiment of the optical element of the present invention.

FIG. 5 is a diagrammatic illustration of a programmable PASS/INVERT gateembodiment of the optical element of the present invention.

FIGS. 6A-6B are diagrammatic illustrations of a programmable branchingelement embodiment of the optical element of the present invention.

FIG. 7 is a diagrammatic illustration of an optical temporary memory orsignal time delay in accordance with the present invention.

FIG. 8 is a diagrammatic illustration of a parallel memory architecturein accordance with the present invention.

FIG. 9 is a diagrammatic illustration of a programmable logic array inaccordance with the present invention.

FIGS. 10A and 10B are top and side views of an array of optical elementswith channel waveguides between elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with one aspect of the present invention, parallel opticaldigital processing is achieved utilizing multiple-face optical logicdevices. Referring to FIGS. 1A-1C, an optical element basicallycomprises a bistable light-responsive element 12 having multiple sidefaces 18. At least two of the faces constitute input faces 20 forreceipt of non-collinear light beams or signals I_(i), i.e., lightsignals having greater than approximately a 15° angle of separation. Atleast one of the faces other than the input faces constitutes acorresponding at least one output face 22 from which light beamstransmitted through element 12 are emitted as output signals I_(O). Allof the input signals I_(i) may constitute data signals, as shown inFIGS. 1A-1C, but as is described in more detail hereinbelow, one of theinput signals preferably constitutes a control or program signal I_(p)for controlling the operations performed by a gate or switch 10.

Optical element 10 is further configured to have an optically-inducednon-linear susceptibility to light signals at a predetermined wavelengthtransversely propagated through light-responsive element 12 such that atleast one portion or cell of element 12 switches between two stablestates depending on the total light intensity of the proper wavelengthin the cell. Thus, when the total light intensity in element 12 is lessthan a predetermined threshold level or trigger intensity I_(th), theelement 12 is in its OFF state, wherein passage of signals through theelement 12 is prevented; and when the total light intensity is equal toor greater than trigger in tensity I_(th), the element 12 is in its ONstate, wherein passage of light signals through the cavity is permitted.

In the preferred embodiment, the two stable states are due to anessentially flat response to light intensity over two distinct intensityregions, and a highly sensitive response to light intensity at or aroundthe trigger intensity, as shown in FIG. 2. There may be a hysteresiseffect, as shown in FIG. 3, in which the actual response at and near thetrigger intensity may be effected by the optical history of element 12.It is appreciated that these response graphs of FIGS. 2 and 3 arerepresentative, and that the actual response may differ. For example,the higher response may correspond to a lower intensity, and theresponse need not be a monotonic function of the total light intensity.

It is preferable that element 12 have at least one optical resonantcavity (not shown) and an optically nonlinear material (not shown)within said resonant cavity, said nonlinear material having a parameter,such as refractive index, which varies nonlinearly with the totalintensity. The Airy function of such an embodiment is conducive toproperties desired in the present invention.

One or more multi-dimensional bi-stable Fabry-Perot cavities made fromsuitable available semiconductor materials, including InSb, ZnS, ZnSe,ZnTe, CdS, CdTe, GaAs, CuCl₂ and the ternary and quaternarysemiconductor alloys, for example, may also advantageously constituteelement 12. It will also be appreciated that while hexagonal andrectangular exemplary embodiments of optical element 10 have been shownin FIGS. 1A-1C, any geometry providing flat faces, as shown in FIG. 1D,is suitable. As shown diagrammatically in FIG. 1A, selected faces 18 ofoptical element 10 advantageously are mirrored, as is conventional.

An array of the optical elements 10 according to the present inventionmay be fabricated employing standard fabrication techniques for channelwaveguides using currently known art lithography techniques. In thealternative, ion implantation and dopant diffusion could be used. Asshown in FIGS. 10A and 10B, these techniques permit the fabrication ofoptical waveguides 70 and optical logic devices 10 having differentindices of refraction than the substrate 72.

Preferably, the input light beams/signals strike directly andperpendicularly on the input faces and the input faces should eachconstitute one side of a resonant Fabry-Perot cavity. Other than in theresonant cavities, there should not be any processing of the signalsbetween the input ports and the output ports, such as by mirrors orlenses.

The output signal should be suitable for use as an input signal byanother optical element according to this invention. In other words, theoptical elements are cascadable. They employ frequency standards andintensity standards corresponding to ON and OFF states. It is understoodthat means, such as "holding beams," may be employed by persons skilledin the art to fine tune the response of element 10. It will also beunderstood that timing, clock, and storage means may be employed bypersons skilled in the art to synchronize signals in the system.

It is preferable that the beams be transmitted directly between theelements, without the use of fibers, mirrors or lenses, and with onlyminimal processing, such as for amplification, correction of corruption,or in general, conformance with standards.

As mentioned above, in accordance with a further aspect of the presentinvention, operation of an optical element 10 to perform predeterminedlogic and other operations is controlled by using the input signal toone of the input faces 18 as a program signal I_(p) ; and further bymodifying the configuration of light-responsive element 12, as describedin more detail hereinbelow. Referring specifically to FIG. 4, AND and ORlogic operations can be obtained using an optical element 200 having thesame construction as element 10 described hereinabove with two or moredata input signal I_(i) and one program signal I_(pl) (two data inputsignal I_(ia) and I_(ib) are shown). The intensities of data inputsignal I_(i) are selected to each equal at least 1/2, but less than thefull trigger intensity I_(th), that is 0.5I_(th) ≦I_(ia),b <I_(th).Consequently, when the intensity of program signal I_(pi) is set equalto zero, true AND gate operation is achieved, i.e., switch 200 istriggered ON and outputs I_(oa) and I_(ob) are produced only when bothdata input signals I_(ia) and I_(ib) are present (ON). By setting theintensity of program signal I_(pl) to also be 0.5I_(th) ≦I_(pl) <I_(th),inclusive OR gate operation is achieved, i.e., switch 200 is triggeredON and the corresponding output I_(oa), I_(ob) is produced when eitherdata input signal I_(ia), I_(ib) is present (ON), and switch 200 is OFF,producing no output, when neither data input signal is present.

It will be appreciated that an AND gate (not shown) may be similarlyobtained by employing an optical element according to the presentinvention, which optical element has 2 input faces and 1 output face,and is designed to operate as the above-described AND/OR gate withoutany program signal I_(pi) or program beam or a face for input of same.

It will also be appreciated that a dedicated OR gate may be implementedby using the aforementioned AND/OR gate with a steady beam of intensity0.5I_(th) ≦I_(pl) <I_(th).

Referring specifically to FIG. 5, INVERT/PASS logic operation isachieved in accordance with the present invention as follows. A compoundoptical element 300 is formed with a light-responsive element 12 havingtwo portions with substantially equal optically variable nonlinearrefractive indices N₁ and N₂ arranged so as to form two separatelyswitchable cells 32 and 34 defining an interface 36 extending obliquelywith respect to the signal path of one of the data input signals I_(i)(e.g., I_(ib) as shown in FIG. 5) and transversely with respect to aprogram signal I_(p2) as shown.

Two output ports O₁ and O₂ are provided on INVERT/PASS element 300. Theelement 300 is designed so that if the program signal is OFF and thedata signal is ON, then the refractive index N₁ for cell 32 is less thanthe refractive index N₂ for cell 34. An ON data signal would bereflected at interface 36 and would appear at output port O₂. TheINVERT/PASS gate 300 is further designed so that if the program signalis ON and the data signal is ON, then the refractive indices N₁ and N₂are essentially equal, and so that cell 32 is in the transmit mode. TheON data signal would be transmitted through interface 36 and cell 32,and would appear at output port O₁. Following is the truth table forthis device:

    ______________________________________                                        Input                O.sub.1   O.sub.2                                        ______________________________________                                        Data OFF, Program OFF                                                                              OFF       OFF                                            Data ON, Program OFF OFF       ON                                             Data OFF, Program ON OFF       OFF                                            Data ON, Program ON  ON        OFF                                            ______________________________________                                    

It can be seen that if the program signal is OFF, then the state ofoutput O₂ corresponds to the state of the input data, whereas if theprogram signal is ON, then the state of output O₁ is the inverse of theinput data state.

Referring specifically to FIGS. 6A and 6B, data line branching isachieved in accordance with the present invention using a compoundoptical element 400 similar in construction to switch 300 describedhereinabove, but with the interface 46 between cells 42 and 44 orientedtransversely to program signal I_(p3) and obliquely with respect to bothdata input signals I_(ia) and I_(ib). When program signal I_(p3) is notpresent (OFF) (FIG. 6A), then whichever input signal I_(ia), I_(ib) ispresent will be reflected by interface 46 (since only the correspondingcell 42, 44 is triggered ON, creating unequal refractive indices in thetwo cells), thus producing output signals I_(oa) and I_(ob) withtransposed data paths. When program signal I_(p3) is present (ON) (FIG.6B), both cells 42 and 44 are triggered ON, and both input signalsI_(ia), I_(ib) will respectively pass directly through switch 400without reflection at interface 46 to respectively produce correspondingoutput signals I_(oa), I_(ob) in the same data paths.

Referring specifically to FIG. 7, signal time delay or temporary memorystorage can be achieved in accordance with the present invention byproviding an array 500 of gates/switches 51-56 having the constructionof branching switch 400 described above and arranged to successivelybranch the data path of an input data signal I_(i) in a closed loop backto a starting switch, e.g., switch 56, of the array 50. Thus, a datasignal can enter the loop at any switch in the array 50, and can beretrieved from the same or a different switch in the loop simply byproviding a program signal I_(p4), as shown at switch 56, to cause thecirculating signal I_(i) to pass directly through the fully ON switchwithout reflection at the switch interface.

It will be appreciated that memory storage can also be achieved inaccordance with the present invention using biased bistable switches aswell as the optical closed loop arrays of nonbiased switches describedabove. In either case, the memory state can be determined by thecondition of the switch/array. To provide maximum parallelism in theoperation of optical computer architectures in accordance with thepresent invention, the memory storage area of a processor advantageouslyis arranged such that all memory cells (switches or arrays) may be readsimultaneously. As shown diagrammatically in FIG. 8, this is achieved inaccordance with the present invention by arranging together on one plane60 in a common area the optical elements of the present inventionconstituting the memory cells 62. For example, the common area may bethe terminus of a series of data paths from a logic switch array 61. Afurther array of optical elements or electrical photoreceptor devices 64is arranged in a separate plane 66 beneath memory cells 62. Since thememory cells 62 can be designed to act as Fabry-Perot cavities betweentheir top and bottom faces, an array of memory cells 62 can be readsimultaneously by illuminating the entire array by a single readinglight beam I_(m) having an intensity less than the trigger intensityI_(th) " of the memory cells 62 applied to the top faces of the memorycells. The cells 62 of the array which are ON transmit the reading beamI_(m) light to the underlying array of devices 74, while the cells 62which are OFF do not. If optical elements constitute devices 64, then anew set of logic operations could be commenced with the light signalstransmitted from memory cells 62. If photoreceptors constitute devices64, the electrical outputs produced by the photoreceptors could be usedto interface with a host electronic computer.

Other similar optical logic gates may be readily designed in accordancewith the present invention.

To provide optimal parallel logic processing in accordance with thepresent invention, the AND/OR, INVERT/PASS and branching elementswitches 200, 300 and 400 described hereinabove preferably are arrangedin sequence as shown in FIG. 9 to form programmable logic unit arrays700 which define at least two parallel data paths A and B and whichperform successive logic operations on data signals travelling along thedata paths A, B. As is also shown, logic unit arrays 700 advantageouslyare arranged so that the respective switches 200, 300 and 400 formcolumns, with the switches in each column being controlled by a commonprogram signal I_(p1), I_(p2), I_(p3), and with a separate set of datapaths A, B addressing one switch per column so that data is propagatedacross columns. Consequently, in accordance with the present invention,data can be propagated in parallel along a pair of data paths through aprogrammable logic array and can interact according to program signals.As many pairs of data paths as desired can be provided simply byextending the length of the switch columns, subject only to the need toboost the program signal power for very long column lengths. Similarly,the number of operations performed in each pair of data paths is limitedonly by the need to provide regular boosting of data signal intensities.Further, for more complex data processing, the number of addressabledata paths in each logic unit array 700 can be increased simply bychanging the geometry of the optical elements 200, 300, 400, such as byusing octagonal or 12-sided configurations instead of the illustratedhexagonal configuration.

It is understood that other similar digital optical computing systemscan be readily designed in accordance with the present invention. Forexample, switching elements may serve to control program branching anddata flow. This invention may be readily adapted for vector processing,parallel processing, pipelining, and neural networks.

It will be appreciated from the foregoing that the present inventionprovides intrinsically parallel optical switch elements because they maybe addressed simultaneously by several non-collinear, independentoptical signals which can be separated at the output of a switch, andbecause an entire array of such switches can also be addressedsimultaneously with a single light beam normal to the plane of theswitches. The planar design of the optical switches of the presentinvention is also compatible with conventional integrated opticsgeometry for placement on a processor board or microchip.

It will be further appreciated that the ability to readily selectivelycontrol the operations performed by the switches of each logic unitarray 700 using program signals greatly increases the flexibility andcapabilities of microcode programs which exploit the intrinsicallyparallel nature of the optical processing elements. At the same time,the architecture of the present invention is fully compatible with"data-flow" processing since it can handle, simultaneously, a multimodeof data paths.

While the present invention has been described with reference toparticular preferred embodiments, the invention is not limited to thespecific examples given, and other embodiments and modifications can bemade by those skilled in the art without departing from the spirit andscope of the invention.

What is claimed is:
 1. A multiple-face optical device comprising alight-responsive element having multiple faces, at least two of saidfaces constituting input faces for receipt of non-collinear lightsignals and at least one of said faces other than said input facesconstituting an output face from which light signals transmitted throughsaid light-responsive element are emitted; said light-responsive elementbeing further configured to have optically-induced non-linearsusceptibility to light signals transversely propagated through saidlight-responsive element such that at least one portion of saidlight-responsive element switches between two stable optical states independence on the total intensity of the light signals within saidlight-responsive element.
 2. The optical device of claim 1 wherein saidtwo optical states consist of an OFF state, wherein passage of lightsignals through said at least one portion is prevented, when said totalintensity is less than a predetermined threshold; and an ON state,wherein passage of light signals transversely through said at least oneportion is permitted, when said total intensity is not less than saidpredetermined threshold.
 3. The optical device of claim 2 wherein saidlight-responsive element comprises one or more Fabry-Perot resonators.4. Optical switch apparatus for providing storage or time delaytransmission of an optical data signal comprising:a plurality of opticaldevices each comprising a light-responsive element having multiplefaces, and being further configured to have first and second portionspossessing substantially equal light sensitive non-linearly variablerefractive indices, such that each portion switches from a first valueto a second substantially different value in response to transverselypropagated light signals within the portion having a total intensityequal to or greater than a threshold intensity; two of said facesrespectively constituting a data signal input face and a first datasignal output face for said first portion; said first and secondportions being arranged to form an interface extending obliquely withrespect to said data signal input face and said first data signal outputface, such that a data signal having an intensity at least equal to saidthreshold intensity which is applied to the data signal input face ofone of said optical devices will be reflected from the associatedinterface of the switch and outputted from the associated first datasignal output face; said plurality of optical devices being arranged toform a continuous loop data signal path whereby a data signal outputfrom the first data output face of each optical device is received bythe data signal input face of the next optical device in succession; andat least one of said optical devices having a program signal input faceand a second data signal output face, opposite said data signal inputface, forming a part of the second portion thereof, such that a programsignal having an intensity at least equal to said threshold intensityapplied to said program signal input face causes a data signal appliedto the associated data signal input face of said at least one of saidoptical devices to pass through the switch without substantialreflection at the associated interface thereof and to exit from theassociated second data output signal face, rather than continuing tofollow said continuous loop data signal path.
 5. Optical switch multiplecell memory apparatus for simultaneous transfer of data from a pluralityof cells in response to a single optical read signal comprising:aplurality of bistable optical switch means defining an array of memorylocations arranged in a first plane, each of said switch means beingswitchable from a first state, wherein light propagating orthogonally tosaid first plane cannot pass through the switch means, in response totransversely propagating light signals within the switch means having atotal light intensity which equals or exceeds a threshold intensity; anda plurality of photosensitive elements arranged in a corresponding arrayin a second plane spaced from and aligned with said first plane so as toreceive light signals produced by those ones of said switch means whichare in said second state when said plurality of switch means isilluminated by an orthogonally directed optical read signal.
 6. Aprogrammable optical logic array device for parallel processing of atleast one set of first and second non-collinear data signals along firstand second data paths comprising:AND/OR optical device meanscontrollable by a first optical program signal for selectively operatingin an AND or an OR logic mode to produce corresponding first and/orsecond data output signals in dependence on the combination of datainput signals present and the logic mode selected; PASS/INVERT opticaldevice means responsive to one of said first and second data outputsignals from said AND/OR optical device means and controllable by asecond optical program signal for selectively operating in PASS orINVERT modes wherein, respectively, a PASS data output signal isproduced in the same data path when said one of said first and seconddata output signals is present, and an INVERT data output signal isproduced in a different data path when said one of said first and seconddata output signals is not present; and BRANCHING optical device meansresponsive to said PASS and INVERT data output signals from saidPASS/INVERT optical device means and controllable by a third opticalprogram signal for selectively operating to transfer PASS and INVERTdata output signals applied as inputs along the same data path as, or adifferent data path from, the data path on which the applied PASS/INVERTsignal was travelling prior to transfer.
 7. The programmable opticallogic array of claim 6 wherein said AND/OR optical device meanscomprises a single cell light-responsive element having planar top andbottom faces and a polygonal shape defining multiple faces, two of saidfaces constituting input faces for receipt of said first and second datasignals, respectively; two of said faces respectively opposite saidinput faces constituting output faces from which said first and seconddata output signals are respectively emitted; and one of said faces notconstituting an input or an output face constituting a program signalinput face for said first program signal; said light-responsive elementbeing further configured to have optically-induced non-linearsusceptibility to light signals transversely propagated through saidlight-responsive element such that said light-responsive elementswitches from an OFF state, wherein passage of light signalstransversely through said light-responsive element is prevented, and anON state, wherein passage of light signals transversely through saidlight-responsive element is permitted, when the total intensity of thelight signals within said light-responsive element equals or exceeds apredetermined threshold, the value of said threshold relative to theintensities of said first and second data signals and said programsignal being selected such that the intensities of none of said firstand second data signals and said first program signal individually equalor exceed said threshold, but the combined intensities of any two ofsaid first and second data signals and said first program signal atleast equals said threshold, and said AND/OR switch means therebyoperates in said AND logic mode when said first program signal is absentand in said OR logic mode when said first program signal is present.